Pump



y 21, 1963 T. BUDZICH 3,090,312

I PUMP Filed Feb. 9, 1961 5 Sheets-Sheet 1 INVENTOR.

Q 77405052 .BUDZ/CH T. BUDZICH May 21, 1963 PUMP 5 Sheets-Sheet 2 Filed Feb. 9, 1961 INVENTOR. 77405052 5002 /CH y 1963 T. BUDZICH 3,090,312

PUMP

Filed Feb. 9, 1961 5 Sheets-Sheet 3 INVENTO BY lE/CHEY, MNNNY& FARR/N6 TON T. BUDZICH May 21, 1963 PUMP 5 Sheets-Sheet 4 Filed Feb. 9, 1961 INVENTOR. TADEUSZ BUDZ/CH BY RIC/1E}; N-NENNY4 FA BRING 70M ATTORNEYS y 1, 1963 T. BUDZICH 3,090,312

PUMP

Filed Feb. 9, 1961 5 Sheets-Sheet 5 INVENTOR. 740E052 .EUDZ/C/v BY E/CHEKMNENA/YFA/PE/NGTON WWW/7 A ATTOIE EYS United States Patent of Ohio Filed Feb. 9, 1961, Ser. No. 88,142 9 Claims. (Cl. 103-37) This invention relates to hydraulic pumps and more particularly to variable volume hydraulic pumps of the type disclosed and claimed in my co-pending applications, Serial No. 825,005, filed July 6, 1950 for Pumps, Serial No. 17,832, filed March 28, 1966* for Axial Piston Pump Drive and Serial No. 847,512, filed October 20, 1959 for Pump Control Means. Reference is also made to my co-pending application Serial No. 111,946, filed May 23, 1961 for Starting Valve for Variable Displacement Pump and my co-pending application Serial No. 94,465, filed March 9, 1961 for Pump Cylinder Block Dampening Means.

It is among the objects of the present invention to provide apump having a housing, and a cylinder block guided for axial movement within the housing, wherein the cylinder block is provided with a plurality of cylinders and axial movement of the cylinder block within the housing is effective to vary the output volume of the pump and wherein the output volume is reduced in response to predetermined increases in outlet pressure.

It is a further object of this invention to provide a variable volume pump according to the preceding object wherein the cylinder block is provided with control means movable therewith and said control means is maintained in fluid communication with the outlet of the pump.

It is a further object of this invention to provide a pump according to the preceding objects wherein the cylinder block is provided with a pair of inner and outer concentric grooves intersecting the walls of the cylinders in the cylinder block to provide inner and outer fluid inlet ports in the cylinders facilitating the rapid filling of the cylinders and increasing the efficiency of the pump.

It is a further object of this invention to provide a variable volume output pump according to the preceding objects which is constructed and arranged so that when the cylinder block within the housing is moved in a direction to reduce the volume output of the pump, the block forms with the pump housing a dashpot efiectively dampening the cylinder block movements.

t is a further object of this invention to provide a pump according to the preceding object wherein a fluid passage is provided in the wall of the cylinder block in the form of an axial groove and wherein the pump housing is provided with an axially adjustable member arranged to fit within said groove to provide a variable restriction for fluid flow from the dash-pot side of the cylinder block to the inlet side of the cylinders and thus provide a variable dampening of cylinder block movements. The cylinder lock dampening means is claimed specifically in said copending application Serial No. 94,465.

It is a further object of this invention to provide a pump according to the preceding objects which will have a large volume output and wherein the component parts of the pump are constructed and arranged to provide for ease in servicing and adjustment and for rugged construction and long life operation.

It is a further object of this invention to provide a starting valve which will relieve bearing loads as the pump is started. The starting valve is claimed specifically in said co-pending application Serial No. 111,946.

Other objects and advantages relating to this invention will appear from the following description and the appended drawings wherein:

3,990,312 Patented May 21, 1963 FIG. 1 is a sectional elevation through a pump made according to the invention;

FIG. 2 is an end elevation of the cylinder block employed in the pump of FIG. 1;

FIG. 3 is a plan view of the cylinder block shown in FIG. 2;

FIG. 4 is an elevation with parts in section of a modified form of pump showing a variable restrictor device for the cylinder block dampening;

IG. 5 is a sectional view taken as indicated by the line 55 of FIG. 4;

FIG. 6 is a sectional view of the cylinder block of FIGS. 4 and 5;

FIG. 7 is a sectional view of a portion of the pump of FIG. 1 modified to provide means to unload the pump for starting;

FIG. 7a is a view showing the wave spring washers employed in the pump unloader;

FIG. 8 is a sectional view similar to FIG. 7sh0wing the pump as unloaded for starting;

FIG. 9 is a sectional view of the output volume control with a pilot valve moved to a position effective to increase the output volume of the pump; and

FIG. 10 is a view similar to FIG. 9 with the pilot valve moved to a position effective to reduce the output volume of the pump.

Referning to the drawings, the pump of FIG. 1 comprises a housing 6 having a reduced diameter cylindrical portion 7 adjacent the pump outlet 8. The end cap 9 for the housing is provided with the outlet 8 and is'formed to provide an annular shoulder lllarranged to abut an inturned flange portion on the housing 6. The end cap is sealed at 1% and held in position by screws 100. The other end of the pump housing is provided with a cover plate 11 secured to the housing by cap screws 12 and apertured as at 13 to receive the pump drive shaft 14. integrally formed with the drive shaft 14 is an eccentric or cam 15 having an inclined face effective to drive a wobble plate 16 which is restrained against rotation within the pump housing by a guide assembly 17 carried by the wobble plate and riding between a pair of parallel wall members 18 and 19 only one of which shows in the section taken in FIG. 1.

A cylinder block, indicated in its entirety as at 20, is mounted for axial movement toward and away from the outlet 8. The end of the cylinder block 20 most nearly adjacent the outlet 8 is cylindrical in cross-section as indicated at 21 and is arranged to have a free sliding fit within the cylindrical portion 7 of the housing 6. The cylinder block is provided with a plurality of cylinders 22. A like plurality of pistons 23 are arranged to be reciprocated within the cylinders 22 for pumping fluid through reaction pistons 24 through check valve assembly 25 and bore 26 to the outlet 8.

The check valve assembly 25 includes an apertured cage 25a enclosing a spring and check valve plate 25b biased to a closed position as shown by the spring. The valve plate 25!) is unseated by a pumping stroke and the fluid being pumped escapes through the apertures in the side walls of the cage 2511. A passageway 26 leads the pumped fluid from each check valve to the outlet chamber 63. The check valve assembly may be conveniently serviced or replaced by removing the threaded plug 25c.

The inlet ports for the cylinders are formed by an annular outer groove 27 milled in the outer periphery of the cylinder block and an annular inner groove 28 milled at the interior of the cylinder block. The grooves '27 and 28 thus form ports 29 and 30 opening into the cylinders 22. As will be understood by those skilled in the art, when the cylinder block 2%) is in the position shown in FIG. 1 and the piston 23 is reciprocated, the pumping stroke is characterized by its maximum output volume.

3 It will also be understood that when the cylinder block is moved to the left, as shown in FIG. 1, to a position adjacent the end cap 9, the piston 23 will be inefiective to close the inlet ports 29 and 30 in the cylinder 22 and thus the pump will have Zero output volume.

Each piston 23 is normally biased to the right by pis ton spring 23a. A piston rod 23b is interposed between the head of the piston 23 and the wobble plate 16 mounted on the cam 15. The rotation of cam produces an oscillating motion in wobble plate \16 which reciprocates each of the pistons.

The cylinder block is provided with spaced cylindrical surfaces 31 at the end thereof remote from the pump outlet and said cylindrical surfaces may slide along a complementary cylindrical surface 32 at the interior of the pump housing 6. The cylindrical outer surface of the cylinder block 20 is preferably provided with axially grooved or re-entrant areas indicated at 33 and 34 in FIG. 3. The areas 33 and 34 combined with an adjacent recess 35 in the pump housing provide a space for holding a quantity of oil immediately adjacent the outer groove '27 forming the ports 29. This construction results in a quick filling of the cylinders 22 when the pistons 23 are retracted.

A cylindrical opening 36 is formed centrally of the cylinder block so as to provide a space for the storage of a quantity of oil adjacent the inner groove 28 forming the ports 30 in the cylinders 22. It will be understood that the pump housing is provided with an inlet 38 and that the interior of the pump housing is filled with oil at a low or inlet pressure. 7

The cylinder block 20, when moved to the left as shown in FIG. 1, displaces the fluid between the cylinder block and the end of the housing. The flow of fluid from this space is through passageway 20a. When the cylinder block is moved to the position shown in FIG. 1, the space is filled by a reverse flow through passageway 20a. Thus the cylinder block and housing serves as a dash-pot to dampen the movements of the cylinder block.

A plate 40 is arranged adjacent the end cap 9 and is apertured to receive the reaction pistons 24. Each of the reaction pistons 24 at the end thereof adjacent the check valve assembly 25 is provided with a coil spring 41 retained on the reaction piston by a snap-ring 42. The plate 40 is secured to the end cap 9 by means of screws or the like 43 and thus the spring 41 is confined and biased so as to urge the reaction piston into sealing engagement with the reduced end face 44 of the check valve member 45. As described in detail in my said co-pending application Serial No. 825,006, filed July 6, 1959, the reaction pistons 24 are maintained in sealing engagement with the check valve inlet member 45 and yet are mounted for limited radial movement so as to accommodate manufacturing variations and permit each reaction piston to be individually seated with respect to its check valve. As pointed out in said co-pending application, this construction permits freedom of alignment and relieves the cylinder block from stresses which might otherwise be imposed by the reaction pistons or the driving pistons 23.

The axial travel of the cylinder block 20 to its maximum volume output position is limited by the abutment at with a support member 51. The member 51 is provided with a cylindrical boss section 52 terminating in a housing 53 for hearing 54 which supports the stub shaft 55 of the eccentric or cam 15. The boss 52 is centrally apertured at 52a and supports therein the neck 56 of a cylinder 57 which is held in place by a snap ring 56a and forms a part of the control means for the pump. I The support member. 51 is apertured in alignment with each of the cylinders 22 so as to accommodate the pistons 23.

'The cylinder block 20 is normally biased to maximum output position by a coil spring 60' mounted. on a boss 61 on the end cap 9 and interposed between the end cap 9 and the bottom of the conical chamber 62 formed in the cylinder block. Generally speaking, the control mechanism is effective to overcome the bias of the spring 60 in response to a predetermined high fluid pressure in the outlet chamber indicated at 63.

The control assembly, indicated in its entirety as at 65, includes a body section 66 which is cylindrical at its midportion and is provided with O-rings 67 and a snap-ring 68 to hold the control assembly in position in a central aperture 65a in the cylinder block 20. The control assembly 65 includes a tubular portion 69 extending axially of the pump to the right as viewed in FIG. 1 and tubular portion 69 is telescopically arranged within the cylinder 57 carried by the support member 51.

The pump control assembly 65 includes a pilot valve plunger 70 which is illustrated in a neutral position in FIG. 1. With the pilot valve 70 in its neutral position, fluid is held in the annular chamber 71, passageway 72 and in the control chamber 73. The control chamber '73 is provided with an apertured plug '74 whereby aperture 75 conducts fluid into the reaction chamber 76. A spring 78 within the control chamber 73 normally biases the pilot valve assembly to the left as viewed in FIGS. 1, 9 and 10.

The right-hand end of the plunger 70 is fitted with a cap member 80 and the spring 78, by Way of abutment washer 79, ball 81 and cap 80, normally biases the plunger assembly to the position shown in FIG. 9. To accomplish the left-hand travel of the plunger 70 it will be appreciated that the spring 78, as supplemented by the fluid pressure in the chamber 73, must overcome the fluid pressure in the outlet chamber 63 effective over the area of the plunger 70. The control assembly 65 receives fluid pressure from the outlet chamber 63 by a transfer tube 82 which is slidably mounted in an axial bore in the end cap 9. The transfer tube 82 is provided with an axial bore 83 which is aligned with an axial bore 84 in a fitting 85 carried by the body 66, and thus fluid pressure in the outlet is effective over the area of the cross-section of the pilot valve plunger 70.

A spring 86 is arranged to surround the transfer tube 82 and bias it against the end face of the fitting 85. The spring pressure supplemented by the Wall area of the transfer tube subjected to outlet pressure provides a pressure assisted seal between the reduced end portion 87 of the transfer tube 82 and the fitting 85.

Referring to FIG. 9, it will be understood that with the pilot valve plunger 70 moved to the position shown, fluid in the control chamber 73 and in the reaction chamber 76 may be discharged therefrom by way of passageway 72, chamber 71, thence through passageway 88 into the low pressure side of the pump housing 6. It will be understood that the spring 60 is continuously biasing the cylinder block 26 and the control 65 carried thereby to the right as viewed in FIG. 1 and the spring 60 is thus seeking to decrease the volume of the reaction chamber 76 and cause the pump to assume its maximum volume position.

Referring to FIG. 10 of the drawings, it will be observed that the pilot valve plunger 70 has been moved to the right so as to overcome the bias of spring 78 as supplemented by the fluid pressure in control chamber 73. This is a condition that would occur in response to a predetermined high pressure such, for example, as 2000 pounds per square inch in the outlet chamber 63. It will be observed that with the plunger 70 in the position shown in FIG. 10, such high pressure fluid flows from the outlet through the transfer tube 82, thence along the space around a left-hand end of the plunger 70, thence into the annular chamber 71, passageway 72 and into control chamber 73. This high pressure fluid flow is effective to increase the volume of chamber 76 and move the cylinder block to the left and thus decrease the output volume.

The control apparatus embodied in the pump of the instant application provides a number of advantages related to accurate response and efiiciency. It will be observed that the transfer tube 82, which is subjected to outlet fluid pressures in the discharge port 63, is arranged to follow the end piece fitting 85 which is carried by the control assembly 65. It will be noted that the control assembly 65 is permanently secured to the cylinder block 20 and moves with it. A reduced area, as at 87, on the end of the transfer tube 82 bears in sealing contact with the end of the face of the fitting 85, and thus there is a positive force during the pump operation holding the transfer tube 82 against the end piece 85, which provides a seal for high pressure oil.

The spring 86 maintains the transfer tube in contact with the end piece 35 when the pressure in the discharge port 63 is at a low or zero pressure. Fluid pressure from the discharge port as is continuously supplied through the passageway 83 of the transfer tube to the end of the pilot valve plunger '76 working axially at the interior of the control assembly es. At the same time the fluid pressure in the outlet chamber 63 acts at the end of the tube 82 providing a positive force normally biasing the cylinder block 2% from left to right as viewed in FIG. 1. This biasing force to the right is augmented by the preload in the spring 69. With no pressure available in the outlet chamber 63, the spring 60 will maintain the cylinder block in its maximum output position shown in FIG. :1 where its movement is limited by engagement with sup- :port plate 51.

The combined force of the hydraulic force on the transfer tube and the spring 64 is then opposed by the force resulting from the cross-sectional area of the piston 69 as multiplied by the control pressure existing in the reaction chamber 76. It will be noted that the control cylinder 57 is anchored to the support member 51 which thus provides a base or fulcrum for the control operations. Accordingly, a generation of pressure in the chamber 76 with the consequent increase in the force acting across the area of the tubular portion 69 of the control assembly 65 will oppose the forces acting from the opposite direction, namely, the forces developed by fluid pressures in the outlet chamber and the preload in the spring 60.

The spring 86 surrounding the transfer tube d2 provides alow force level and may be neglected insofar as balancing the forces acting on the control assembly.

The pre-load in the spring 78 must be over-balanced by the pressure acting on the end of the pilot valve plunger 76 in order to enable the center land on the plunger '70 to admit high pressure oil into the space 73 and thence through the passageway '75 into the space 76.

in order to obtain the desirable prompt response in the pump control the mass of the cylinder block 29 must be moved for the full length of its travel in as short a time as possible. Accordingly, although the force level available from the control when considering the area of the piston 69 and the level of the pressure in the space 76 is quite high, the response of the pump when going to zero fiow to maximum fiow depends on the pre-load in the springs and the rate of the springs. In the instant design the force available to accelerate the cylinder block 2% from left to right is dependent upon the cross-sectional area of the transfer tube 82. The larger the cross-sectional area of the transfer tube 82,, the higher the force transmitted to the cylinder block trying to move it from left to right. Under such circumstances it is not necessary to provide a high pre-load in the spring 60.

The force effective to move the cylinder block 2t) from left to right is a composite of the hydraulic force which is steady at the outlet and a spring force and this combination provides a very low combined rate characteristic. For example, we may assume that the cross-sectional area of the transfer tube 82 is sufi'ciently large to provide a force equivalent to 300 pounds acting directly on the cylinder block 71. With this first assumption we will assume that the pre-load in the spring 6%] is five pounds and the rate of the spring 69 is about five pounds per inch. In the example assumed, when combining those two forces acting in the same direction, 'we obtain a force equivalent to 305 pounds pre-load in the extended position and 310 pounds in the retracted position with about one inch of cylinder block travel. Accordingly it will 'be understood that the combination of fluid forces and spring pre-loads give a rate of control which would be difficult or impossible with springs alone. It will also be understood that springs alone would not provide a stable control arrangement.

It will also be appreciated that the control here provided not only gives a fast response to changes in pressure at the outlet, but also provides a control operating with low pressure differentials.

A modified form of pump is illustrated in FIGS. 4, 5 and 6. In this form of my invention the pump housing 1430 is provided with a cylinder block 101 mounted to move axially within the housing to vary the output volume. As in the embodiment earlier described, the end of the housing is provided with an end cap 102 having a check valve assembly 103 aligned with each of the reaction pistons 1G4 arranged within the pumping cylinder ms. The check valve assembly 193 is constructed and anranged to operate like the check valve assembly 25 in the embodiment first described.

As in the earlier embodiment, the cylinder block 101 is provided with an inner annular groove 1% to provide 'an inner cylinder port 107 and an outer annular groove 1% to provide an outer cylinder post 109. In the cylinder block of this form of pump that portion of the cylinder block remote from the check valve assembly 103 is provided with a cylindrical surface 116 having a sliding fit with a complementary surface 111 on the housing. The end of the cylinder block 101 adjacent the check valve is provided with a cylindrical surface 112 having a sliding fit on a complementary cylindrical surface 113 at the interior of the housing.

The outer periphery of the cylinder block 101 is provided with an axial groove 115 which is adapted to receive a plug 1-16 carried by the housing 1%. The end of the plug 116 accessible at the exterior .of the housing is provided with an socket head as at 117 and the plug 116 is provided with an O-ring seal as art 118. The groove 115 provides a path for the flow of fiuid from the space 128 between the cylinder block 101 and the end cap 102 as the cylinder block is moved axially to vary the output volume. 'The effective cross-sectional area of the passageway for "fluid may be varied by turning the plug 116 on its'threaded connection in the housing to change thedepth of engagement of the plug in the groove 115, and accordingly the dampening effwt or dash-pot effect on the cylinder block movements may be controlled to suit a particular pump operation.

This form of pump is preferably provided with the control apparatus 65 arran ed to vary the output volume in response to predetermined changes in the output pressure. This form of pump is provided with a supporting member corresponding generally in function and arrangement to the member 51 in the first embodiment. The member 125 is apertured at 126 to conduct pump fluid into the groove 1% at the interior of the cylinder block. In this form of pump a reaction cylinder 127 surrounds the-tubular portion 69 of the control assembly -65. The cylinder 127 is mounted in a central aperture in the supporting member 125 and is provided with a shoulder 12% arranged to bear against the member 125 around its central aperture. The cylinder 127 encloses the reaction chamber 76 and otherwise operates as in the embodiment first described.

A pump made according to the forms of FIGS. 1 and 5 may be provided with a pump unloading device such as that illustrated in FIGS. 7 and 8. Those, skilled in the art will appreciate that when the pump isnot operating, spring loadingsapplied to the piston rods tend tosqueeze out the oil film on the normally lubricated surfaces,

especially on the cam drive surfaces of the pump. It is particularly desirable to have means to unload the pump, that is, .to relieve the pump from high bearing loads '7 'at the initiation of the pump operation. In FIG. 1, I have illustrated the drive shaft 14 as being mounted in anti-friction bearings 2 and 3. The anti-friction bearing assembly at 3 is preferably of the type disclosed in my oo-pending application Serial No. 17,832, filed March 28, 1960. An anti-friction or roller bearing assembly indicated at 4 is interposed between the inclined surface of the cam 15 and the wobble plate 16. It will be understood that plain bronze bearings may be used in place of the bearings 2, 3 and 4 and that where such plain bearings are used, it is desirable to relieve the surfaces of high starting loads, particularly where the pump has been idle for some time and the spring loading has squeezed out the oil film normally effective to lubricate such surfaces. Such plain bearings are shown in my co-pending application Serial No. 825,005, filed July 6, 1959, and my co-pending application Serial No. 847,512, filed October 20, 1959, illustrates another form of pump unloading device.

, In the form of pump unloader shown in FIGS. 7 and 8, the cylinder block 150 is provided with an output volume control assembly indicated in its entirety as at 151. It will be understood that the assembly 151 includes an axially movable pilot valve plunger constructed and arranged as the plunger 70 in the embodiment previously described.

The pump housing end cap 152 is provided with an outlet chamber as at 153 and a transfer tube 154 places the outlet chamber in communication with the control assembly 151. The spring 60 is arranged as in the previous embodiment and normally biases the cylinder block 150 and the control assembly 151 carried thereby to the right. It will be observed that movement of the cylinder block from maximum to minimum volume position is accommodated by movement of the transfer tube 154 moving in and out of the outlet chamber 153.

During normal operation of the pump the inner end 155 of the transfer tube 154 bears against an inlet member 156. Hydraulic fluid at pump inlet pressure surrounds the transfer tube in the space 157 and the pressure existing in the outlet chamber 153 is effective to move the transfer tube 154 to the right compressing a pair of wave type annular spring washers 158 which are axially separated by a plain washer 165. A coil spring 159 surrounds the transfer tube 154 and supplements the action of the outlet pressure in urging the transfer tube 154 against the inlet member 156 and thus supplements the outlet pressure in compressing the wave spring washers 158. Normally the wave spring washers 158 exert a greater expansive force than the coil spring 159 and, in the absense of outlet chamber pressure, the transfer tube 154 is moved to the position shown in FIG. 8. This movement of the transfer tube 154 effected by the wave type annular spring washers 158 results in a gap, as at 160, to permit outlet fluid to escape outwardly through the wave spring washers 158 and thence through apertures 161 formed in the retainer member 162 surrounding the wave type spring.

'It will be observed that the down-turned end 163 on the member 162 engages the spring retainer 164 on the transfer tube 154 and thus limits the movement of the transfer tube in response to the wave springs 158.

From the description of the structure of FIGS. 7 and 8, it will be understood that when the pump is idle the wave spring washers 158 will be effective to provide the gap 160 and thus fluid pressure at the outlet may escape into the space 157 and the pumping pistons are relieved of pumping loads at the start of the pump operation. After the drive shaft 14 and the eccentric cam 15 carried thereby have made a few revolutions, the volume being pumped by the pistons will exceed the volume which may escape through the gap 160 and thus fluid pressure in the outlet chamber 153 will be increased until it is effective over the area of the transfer tube to move the parts to the position shown in FIG. 7. In this position a tight sealing engagement is made between the transfer tube and the inlet member 156 which conducts outlet fluid into the control assembly 151.

Although I have shown and described certain pump apparatus in considerable detail, and have described unloading and dampening features in detail, it will be appreciated by those skilled in the art that numerous modifications may be made therein without departing from the scope of the invention as defined in the following claims.

What is claimed is:

1. A variable volume pump comprising a housing, said housing having a cylindrical interior wall portion, a cylinder block mounted in said housing, said cylinder block having exterior portions thereof cylindrical and mounted for axially sliding movement within said cylindrical portions of said pump housing, an outlet chamber at one end of the housing, control means to move said cylinder block axially within said housing from a position of maximum volume output to :a position of minimum volume output, said control means being mounted centrally of the cylinder block and including a spring arranged to bias said cylinder block to a position of maximum output, said control means having an elongated hollow transfer tube projecting into said outlet chamber, said transfer tube arranged for axially sliding movement through a wall in said outlet chamber, said control means having an axially slidable plunger, said plunger having one end thereof subjected to outlet fluid pressure and having the other end thereof spring biased toward the outlet chamber, said control means having a reaction chamber enclosing one end of said plunger, and valve means on said plunger to admit outlet fluid pressure to said reaction chamber in response to movement of the plunger away from said outlet.

. 2. A variable volume pump comprising a housing, said housing having an interior wall portion circular in crosssection, a cylinder block mounted in said housing, said cylinder block having exterior portions thereof circular in cross-section and having a sliding fit within said circular portions, said housing having an end wall provided with an outlet chamber, control means to move said cylinder block axially within said housing from a position remote from said outlet chamber to a position adjacent said outlet chamber, said control means including a spring arranged to normally bias said cylinder block to a position remote from the outlet chamber, said control means being carried by the cylinder block and having an elongated transfer tube projecting from one side of said cylinder into the said outlet chamber, said transfer tube arranged for axially sliding movement in said outlet chamber, said control means having a plunger mounted therein and being movable relative to the cylinder block, said plunger having one end thereof open to outlet fluid pressure, said other end of said plunger having a spring to bias the plunger against said outlet pressure, and valve means on the plunger to determine cylinder block move ment in response to outlet pressure changes.

3. A variable volume pump comprising a housing having an inner wall portion providing a cylindrical surface, an end cap secured to one end of said housing, an outlet chamber in said end cap, an end cap at the other end of said housing having a drive shaft mounted therein, a fluid inlet for said housing to fill the interior of said housing with fluid at low pressure, a cylinder block having an exterior portion in the form of a cylinder and arranged to bear against the inner wall of said housing and be guided axially therein, said cylinder block having pumping cylinders therein and being movable in the housing toward said outlet to a position of minimum volume output and being movable away from said outlet chamber to a position of maximum volume output, a control assembly mounted centrally within said cylinder block and being movable therewith toward and away from said outlet chamber, said control assembly including fluid motor means adapted to shift said cylinder block in said pump housing between the maximum and the minimum dis placement positions, said control assembly including valve means to control the flow of fluid to and from said fluid motor means, a transfer tube operatively connected to said control assembly and projecting axially therefrom into said outlet chamber, said tube being subjected to outlet chamber fluid pressure and conducting outlet chamber fluid into said control means carried by the cylinder .block.

4. A variable volume pump comprising a generally cylindrical housing, an end cap secured to one end of said housing, an outlet chamber in said end cap, an end cap at the other end of said housing having a drive shaft journalled therein, a fluid inlet for said housing to fill the interior of said housing with fluid at low pressure, a cylinder block having an outer peripheral portion in the form of a cylindrical surface and arranged to bear against the inner cylindrical wall of said housing and be guided axially therein, said cylinder block having pumping cylinders therein and being movable in the housing toward said outlet chamber to a position of minimum volume output and being movable away from said outlet chamber to a position of maximum volume output, means connecting said pumping cylinders to said outlet chamber, a control assembly mounted centrally within said cylinder block and being movable therewith toward and away from said outlet chamber, a transfer tube operatively connected to said control assembly and projecting axially therefrom into said outlet chamber, said tube being subjected to outlet fluid pressure and conducting outlet fluid into said control means carried by the cylinder block, said control assembly including a control piston extending axially therefrom oppositely from said transfer tube and movable with the cylinder block as it moves toward and away from the outlet, a reaction cylinder enclosing said control piston, an elongated movable valve plunger mounted within said control means having one end thereof open to fluid pressure at the outlet and the other end thereof subjected to fluid pressure Within said reaction cylinder, spring means within said control piston arranged to bias said plunger to a position adjacent said outlet whereby fluid pressure within said reaction cylinder is directed to the interior of said housing, said plunger being moved axially into said control cylinder in response to a predetermined high pressure in said outlet whereby fluid from said outlet is directed into said reaction cylinder and said fluid pressure in the reaction cylinder is effective to move the cylinder block to a position of minimum output.

5. A variable volume pump comprising a housing, an end cap secured to one end of said housing, an outlet chamber in said end cap, an end cap at the other end of said housing having a drive shaft journalled therein, a fluid inlet for said housing to fill the interior of said housing with fluid at low pressure, a cylinder block mounted in said housing and guided axially therein, said cylinder block being movable in the housing toward said outlet chamber to a position of minimum volume output and being movable away from said outlet chamber to a position of maximum volume output, a control assembly mounted on said cylinder block and being movable therewith toward and away from said outlet chamber, said outlet chamber having a tube opening therein, a transfer tube operatively connected to said control assembly and projecting axially therefrom into said tube opening, said transfer tube being subjected to outlet fluid pressure and conducting outlet fluid into said control means carried by the cylinder block, said control assembly including a control piston extending axially therefrom and movable with the cylinder block toward and away from the outlet, a reaction cylinder fixed within the housing and arranged to surround said control piston, valve means responsive to fluid outlet pressure, spring means within said control piston arranged to bias said valve means to a position releasing fluid pressure from said reaction cylinder to the interior of said housing, said valve means being moved in an opposite direction in response to a block to a position of minimum output.

6. A variable displacement pump comprising a pump housingdefining a fluid chamber, an inlet to said chamber and an outlet centrally located on the end of said housing, a cylinder block mounted in said housing for sliding movement along a longitudinal axis, a plurality of cylinder bores in said cylinder block, a piston in one end of each of said cylinder bores, drive means for reciprocating said pistons, an expansible chamber fluid motor adapted to shift said cylinder block along said axis, said motor including a cylinder element and a piston element, one of said elements being mounted on said housing, the other of said elements being mounted on said cylinder block, a control valve centrally mounted on said cylinder block and adapted to control the flow of fluid to and from said fluid motor, a transfer tube slidably journaled in said housing and opening at one end into said pump outlet, said transfer tube being connected at the other end to said control valve for movement therewith as said control valve and cylinder block move axially with respect to said pump housing.

7. A variable displacement pump comprising a pump housing defining a fluid chamber, an inlet to said chamber and an outlet centrally located on the end of the said pump housing, a cylinder block mounted within said housing for sliding movement along a longitudinal axis, a plurality of cylinder bores in said cylinder block, a piston in one end of each said cylinder bores, drive means at one end of said pump housing for reciprocating said pistons, a web member extending transversely across said fluid chamber intermediate said drive means and said cylinder block, tan expansible chamber fluid motor adapted to shift said cylinder block along said axis, said motor including a cylinder element and a piston element coaxial with said cylinder block, one of said elements being secured to said web member, the other of said elements being mounted on said cylinder block, a control valve centrally located on said cylinder block and adapted to control the flow of fluid to and from said fluid motor, a transfer tube coaxially with said control valve slidably mounted on said pump housing, one end of said transfer tube extending into said pump outlet, and the other end of said transfer tube being connected to said control valve for movement therewith as said control valve and cylinder block slide relative to said pump housing.

8. A variable displacement pump comprising a pump housing defining a fluid chamber, an inlet to said chamber and an outlet centrally located on the end of said pump housing, a cylinder block mounted in said housing for sliding movement along a longitudinal axis, a plurality of cylinder bores in said cylinder block, a piston in one end of each said cylinder bores, drive means for reciprocating said pistons, an expansible chamber fluid motor adapted to shift said cylinder block along said axis, said motor including a cylinder element and a piston element, one of said elements being mounted on said housing, the other of said elements being mounted on said cylinder block, a control valve centrally mounted on said cylinder block and adapted to control the flow of fluid to and from said fluid motor, said control valve having an axial opening on the end adjacent said pump outlet, a transfer tube slidably journaled in the end of said pump housing, said transfer tube extending between said control valve opening and said pump outlet and adapted to conduct fluid from said pump outlet to said control valve, an abut ment face on said control valve surrounding said axial opening, a mating abutment face on said transfer tube adjacent said control valve, and spring means adapted to 1 1 bias said transfer tube into abutting contact with said control valve.

9. A variable displacement pump comprising a pump housing defining a fluid chamber, an inlet to said chamber and an outlet on said housing, a cylinder block mounted in said housing for sliding movement along a longitudinal axis, a plurality of axially extending cylinder bores in said cylinder block, a piston in one end of each of said cylinder bores, drive means for reciprocating said pistons, an expansible chamber fluid motor adapted to shift said cylinder block along said axis, said motor including a cylinder element and a piston element on said axis, one of said elements being mounted on said housing, the other of said elements being mounted on said cylinder block, control valve means operable in response to pressure in said outlet to control the flow of fluid to and from said fluid motor, said control valve being connected to said pump outlet, spring means biasing said cylinder block in opposition to the action of said fluid motor, a fluid pressure biasing 12 member slidably journaled in said housing and extending along said axis, said biasing member having one end exposed to fluid pressure in said outlet and the other end adapted to engage said cylinder block to provide a biasing force on said cylinder block proportional to the outlet pressure and opposing the action of said fluid motor.

References Cited in the file of this patent UNITED STATES PATENTS 7 Taylor Feb. 9 1915 1,128,077 2,678,607 Hufierd et a1. May 18, 1954 2,845,941 Wagner Aug. 5, 1958 2,990,781 Tuck July 4, 1961 FOREIGN PATENTS 140,930 Australia Apr. 23, 1951 ,202,109 France June 20, 1959 

1. A VARIABLE VOLUME PUMP COMPRISING A HOUSING, SAID HOUSING HAVING A CYLINDRICAL INTERIOR WALL PORTION, A CYLINDER BLOCK MOUNTED IN SAID HOUSING, SAID CYLINDER BLOCK HAVING EXTERIOR PORTIONS THEREOF CYLINDRICAL AND MOUNTED FOR AXIALLY SLIDING MOVEMENT WITHIN SAID CYLINDRICAL PORTIONS FO SAID PUMP HOUSING, AN OUTLET CHAMBER AT ONE END OF THE HOUSING, CONTROL MEAN TO MOVE SAID CYLINDER BLOCK AXIALLY WITHIN SAID HOUSING FROM A POSITION OF MAXIMUM VOLUME OUTPUT TO A POSITION OF MINIMUM VOLUME OUTPUT, SAID CONTROL MEANS BEING MOUNTED CENTRALLY OF THE CYLINDER BLOCK AND INCLUDING A SPRING ARRANGED TO BIAS SAID CYLINDER BLOCK TO A POSITION OF MAXIMUM OUTPUT SAID CONTROL MEANS HAVING AN ELONGATED HOLLOW TRANSFER TUBE PROJECTING INTO SAID OUTLET CHAMBER, SAID TRANSFER TUBE ARRANGED FOR AXIALLY SLIDING MOVEMENT THROUGH A WALL IN SAID OUTLET CHAMBER, SAID CONTROL MEANS HAVING AN AXIALLY SLIDABLE PLUNGER, SAID PLUNGER HAVING ONE END THEREOF SUBJECTED TO OUTLET FLUID PRESSURE AND HAVING THE OTHER END THEREOF SPRING BIASED TOWARD THE OUTLET CHAMBER, SAID CONTROL MEANS HAVING A REACTION CHAMBER ENCLOSING ONE END OF SAID PLUNGER, AND VALVE MEANS ON SAID PLUNGER TO ADMIT OUTLET FLUID PRESSURE TO SAID REACTION CHAMBER IN RESPONSE TO MOVEMENT OF THE PLUNTER AWAY FROM SAID OUTLET. 